The conventional helically coiled, wire-type screw thread insert currently available to the industry is provided with a diametrical tang on one of its end convolutions. The tang is constructed so as to be gripped by a special tool projecting through the insert. This then enables insertion of the insert into a tapped hole. After the insertion of the insert the tang must be broken off and removed, otherwise the tang would prevent a bolt from being threaded into the insert. Accordingly, a notch is provided on the inside of the end convolution of the coil near the tang so that the tang may be broken off. The broken tang must be accounted for in certain critical applications, e.g. in electronic equipment in which the loose metal tang could cause an electrical short, also in internal combustion engines where the loose metal tang could cause engine failure. Further, the extraction of such prior art inserts once installed, requires the use of an extracting tool which essentially destroys and thus prevents any reuse of the insert. The removal process can also cause damage to the workpiece.
Tangless helically coiled, wire-type inserts are known and an example of such is described in U.S. Pat. No. 2,363,789 which issued to O. Haas, Nov. 28, 1944. Such an insert, however would require that the end coil, containing the recessed hook, project inwardly in order to avoid causing burrs or shaving the material from the tapped thread in the workpiece hole during the installation of the insert. Any build-up of burrs and shaved material can prevent insert installation or lead to improper installation and an inability to install a bolt therein. The extraction of the Haas-type tangless insert, not designed for ease of removal, requires the use of an extracting tool, which also essentially destroys and prevents reuse of the insert, as well as, causing possible damage to the workpiece.
A problem with both the conventional tang inserts and the Haas tangless insert is that the method used for inserting the insert into a tapped hole requires the operator to manually orient the driving end of the insert. This is necessary before any installation torque can be applied to the driving end of the coiled insert, because the tang or recessed hook is only at one end of such prior art inserts. Despite such prior art inserts, there exists a need in the industry for a helically coiled, wire-type screw thread insert which (1) can be inserted into the workpiece by either end without regard to orientation, (2) does not cause damage to the workpiece during installation as by shaving or similar action, (3) provides a lead-in or piloting action for the bolt insertion, (4) can be subsequently removed without damage to either the insert or the workpiece and, (5) does not require accounting for broken-off tang portions.